1. Field of the Invention
The present invention relates to a manufacturing system for pneumatic tires and, in particular, to an improved method and apparatus for highly efficiently building green tires which are ready for vulcanization to produce radial tires.
2. Description of the Related Art
As known in the art, pneumatic radial tire includes reinforcement in the form of one or more belt members having a high tensile rigidity in their longitudinal directions. Thus, it has been a conventional practice to build green tires for pneumatic radial tires by a two-stage process as disclosed, for example, in U.S. Pat. No. 5,380,384 (or corresponding EP-613767B or JP-A-6-254990), the disclosure of which is hereby incorporated by reference.
In this instance, a green case comprising a carcass ply member and bead core members is formed on a first drum which is for the first building stage. A composite member, which comprises a belt member and a tread rubber member joined with each other, is separately formed and moved by a transfer ring onto the outer surface of the green case. The green case is then inflated into toroidal shape and thereby joined with the belt member. The green case joined with the composite member is held by the transfer ring and moved onto a second drum which is for the second building stage. The second drum comprises side bladders on which sidewall rubber members are wound, and which are inflated so as to urge the sidewall rubber members against the tread rubber member on both side edges thereof.
The above-mentioned known method proved to be particularly advantageous in that pneumatic tires can be manufactured with high productivity and at low cost. This is due to the fact that the work loads are assigned to the first and second stages in a well-balanced manner as to mitigate the difference in the cycle time for the two stages, and the green tires can be thus manufactured within a significantly reduced time. Nevertheless, it would be desirable to further develop the above-mentioned known method in various aspects, with an objective to achieve further improved productivity and cost reduction.
It is a primary object of the present invention to provide improved system for manufacturing pneumatic tires. The present invention ensures that existing manufacturing system can be utilized with minimized investment for the partial modification of the second drum, avoiding requirement for specifically designed arrangement to the extent possible. The system can be operated so as to improve the productivity of green tire building process by achieving well-balanced cycle time required for the first and second building stages while reducing the total cycle time, and to readily allow change in the specification of tires to be produced. The system is particularly suitable for manufacturing pneumatic tires with a higher product quality.
According to one aspect of the present invention, there is provided a method for manufacturing pneumatic tires comprising the steps of:
forming on a first drum a green case in which a carcass ply member and a pair of bead core members are joined together, and holding and moving the green case by a transfer device to a position around a second drum;
expanding a pair of centering elements radially outwards from the second drum and positioning the centering elements with reference to opposite inner sides of a pair of bead portions which are folded radially inwards around the bead core members of the green case held by the transfer device, and then moving the centering elements in opposite directions and thereby urging the centering elements against the opposite inner sides of the bead portions;
expanding a pair of lock elements on radially outer side of the centering elements and urging the lock elements against inner peripheral surfaces of the bead portions so as to fixedly secure the green case to the second drum;
subsequently releasing the green case from the transfer device;
causing the second drum to expand and undergo a width reduction, thereby expanding the green case into a toroidal shape; and
joining sidewall rubber members to said toroidal green case to thereby form a green tire, said sidewall rubber members being wound on a pair of side bladders on the outer side of the lock and expanded and reversed by inflating said side bladders.
Advantageously, the second drum comprises an expandable center drum body having an adjustable width, wherein the pair of side bladders are situated adjacent to the drum body with the centering elements therebetween, and wherein the green case is held in place by accommodating the drum body and centering elements within the green case between the opposite inner sides of the bead portions. In this instance, it is preferred that the centering elements are radially expandable between the drum body and the respective side bladders, and axially movable in opposite directions, wherein the centering elements are expanded so that a clearance is always formed between radially outer most ends of the centering elements and an inner peripheral surface of the green case.
Advantageously, the side bladders have folded ends which are embedded in, and fixedly secured to the lock elements situated adjacent to the centering elements, wherein the sidewall rubber members are wound on the side bladders on the sides of the folded ends while the lock elements are in radially retracted positions.
It is preferred that a substantially constant length of said sidewall rubber members are automatically wound on said side bladders of the second drum during formation of a green case on the first drum, and the green case is transferred to the second drum by passing over the sidewall rubber members while the lock elements are in radially retracted positions.
It is also preferred that the sidewall rubber members are each wound on a smooth surface region and a rough surface region of the sidewall rubber.
Advantageously, those regions of the lock elements, which are urged against the inner peripheries of the bead portions of the green case, are aligned with the edges of the sidewall rubber members which are situated on the folded ends of the side bladders.
It is preferred that the side bladders each comprises a first side bladder section for winding the sidewall rubber member thereon, and a second side bladder section situated adjacent to the first side bladder section, wherein the first and second side bladder sections are sequentially inflated.
Advantageously, a composite member wherein the belt member and the tread rubber member are joined to each other is transferred to a position around the green case which has been fixedly secured to the second drum, and maintained centered with reference to the green case. The green case is then radially expanded and urged against, and thereby joined to the composite member, in such a manner that the side edges of the composite member are folded over, and tightly joined to the green case, and the sidewall rubber members are joined to side edges of the tread rubber member. In this instance, it is preferred that the composite member is formed during formation of the green case.
According to another aspect of the present invention, there is provided an apparatus for manufacturing pneumatic tires, comprising:
a first drum for forming a green case in which a carcass ply member and a pair of bead core members are joined together;
a second drum for forming a green tire in which the green case is joined to a belt member, a tread rubber member and sidewall rubber members;
a transfer device for holding and moving the green case to a position around the second drum;
a pair of centering elements which are expandable radially outwards from the second drum and adapted to be positioned with reference to opposite inner sides of a pair of bead portions which are folded radially inwards around bead core members of the green case held by the transfer device, and also adapted to be moved axially in opposite directions and thereby urged against the opposite inner sides of the bead portions;
a pair of lock elements situated on radially outer side of the centering elements and adapted to be urged against inner peripheral surfaces of the bead portions so as to fixedly secure the green case to the second drum;
means for causing the second drum to expand and undergo a width reduction after the green case has been released from the transfer device, thereby expanding the green case into a toroidal shape; and
means for joining sidewall rubber members to said toroidal green case to thereby form a green tire, said sidewall rubber members being wound on a pair of side bladders on the outer side of the lock and expanded and reversed by inflating said side bladders.
Advantageously, the second drum comprises an expandable center drum body having an adjustable width, wherein the pair of side bladders are situated adjacent to said drum body with said centering elements therebetween, and wherein the green case is held in position by accommodating the drum body and centering elements within the green case between the opposite inner sides of the bead portions.
It is preferred that the centering elements are radially expandable between the drum body and the respective side bladders, and axially movable in opposite directions, wherein the centering elements are adapted to be expanded so that a clearance is always formed between radially outer most ends of the centering elements and an inner peripheral surface of the green case.
Advantageously, the side bladders have folded ends which are embedded in, and fixedly secured to the lock elements situated adjacent to the centering elements, wherein the sidewall rubber members are wound on the side bladders on the sides of the folded ends while the lock elements are in radially retracted positions.
It is preferred that the apparatus according to the present invention further comprises means for automatically winding a substantially constant length of the sidewall rubber members on the side bladders of the second drum during formation of a green case on the first drum, and wherein the transfer device is arranged such that the green case is transferred to the second drum by passing over the sidewall rubber members while the lock elements are in radially retracted positions.
It is also preferred that the sidewall rubbers are each wound on an outer surface of said side bladders which is comprised of a smooth surface region and a rough surface region.
Advantageously, those regions of the lock elements, which are urged against the inner peripheries of the bead portions of the green case, are aligned with the edges of the sidewall rubber members which are situated on the folded ends of the side bladders.
It is preferred that the side bladders each comprises a first side bladder section for winding the sidewall rubber member thereon, and a second side bladder section situated adjacent to the first side bladder section, wherein the first and second side bladder sections are sequentially inflatable.
Advantageously, the apparatus according to the present invention further comprises a belt/tread drum for forming a composite member in which the belt member and the tread rubber member are joined to each other to form a composite member; and a further transfer device for moving the composite member to a position around the green case which has been fixedly secured to the second drum, and holding the composite member centered with reference to the green case. The second drum is expandable so that the green case is radially expanded and urged against, and thereby joined to the composite member. The side edges of the composite member are subsequently folded over, and tightly joined to the green case. The side bladders are operable so that the sidewall rubber members are joined to the side edges of the tread rubber member. In this instance, it is preferred that the belt/tread drum is operable so that the composite member is formed during formation of the green case.